1. Field of the Invention
This invention has relation to door latch apparatus for positively accomplishing the final movement of a door to its closed position in a door frame and for initially positively moving the door from its fully closed position to a position where one edge of the door is entirely clear of the door frame in a structure where considerable force must be applied to engage and disengage a gasket around the periphery of the space between the door and frame.
2. Description of the Prior Art
It is often advantageous to seal a cabinet to diminish the possibility of travel of uninterrupted electromagnetic waves into or out of the cabinet. Microwave ovens are one example of such cabinets, but there are also uses for such cabinets as envelopes sealed against other electromagnetic radiation. Such cabinets can constitute all metal envelopes, and at every junction of the various metal components, electrical continuity between components must be established and maintained.
In order to seal the entrance door of such a cabinet to its door frame, it is known to provide a continous metallic gasket between the door and the door frame. Such gaskets can run around the entire inner periphery of the door frame and are so shaped that when the door is closed tightly, the gasket is firmly compressed between the door and the door frame all the way around the edge of the door and the frame.
In compressing the metallic gasket along the top edge and the bottom edge of the door and door frame, the compression is progressive, inch by inch, as the door is hinged shut. Along the hinged edge and along the latch edge, however, compression of the gasket happens only during the very last movement of the door as it closes. There is no such incremental progression. Thus, a relatively much greater force is necessary to finally push the door shut against the door frame to overcome the bias forces of the metallic spring gasket between the hinged edge and the latch edge of the door and frame. For the same reasons, a greater force of similar magnitude is required to initially move the door from its closed position to position clear of that part of the gasket along the latch and hinge edges.
The concept of a door latch and release apparatus which uses the closing movement of the door handle to forceably draw a door into sealing relationship with respect to its cabinet, and which uses the initial opening movement of such a handle to forceably start movement of the door away from the cabinet is old and well known.
In U.S. Pat. No. 2,557,670 granted to Luft on June 19, 1951, a handle H on a cabinet wall moves a vertical link 60 up and down to pivot a hook 52, 53, 54 of a cam-lock arm 49 into fastening relation with respect to a slot 55 in a keeper bar 56 anchored on a door 18.
To get maximum access to the interior of cabinets of the present invention, the door customarily covers one entire wall of the cabinet. This structure of Luft is not, therefore, adaptable to obtain a substantially firm metallic seal all the way around the door and door frame because of the use of the vertical link sliding up and down the interior of the trunk wall.
U.S. Pat. No. 3,374,018 granted to Lust on Mar. 19, 1968 shows a snap-action catch in which a slidable thrust rod on a cabinet door rotates a hook cam on the door to engage a latch pin on a cabinet. The hook cam structure as shown in this patent, and the similar structures as shown in the patent to Luft, and in the patents discussed below, all present a high friction arrangements. Such structures have been tried and found to be ineffective to provide the force necessary to finally close and initially open electromagnetic radiation-tight cabinets such as used in connection with the present invention.
U.S. Pat. No. 3,464,729 granted to Chambers on Sept. 21, 1969 shows a vertical rod 22 which is rotatably mounted to a door and is controlled by a handle 7. The rod has a cam 2' at the top end and a cam 2 at the bottom end, and as the door is almost shut, the rod is rotated and each of these cams interacts with pins 4 and 5 of seatings 3' and 3 to finally force the door closed. Reversing the action of the handle will initially force the door open slightly.
In the context of the present invention, the dimensions of the cams 2',2 and of the pins 4,5 is such that sufficient powered movement of the latch edge of the door toward the door frame cannot be achieved without going to large and awkward configurations. Perhaps more important, however, is that this mechanism of Chambers is useful to positively position only the very top edge and the very bottom edge of the door to the door frame. Multiple latches cannot be provided along the latch edge of the door at intervals such as is often necessary or advisable in sealing the doors of radiation-tight boxes or cabinets useful with the present invention.
U.S. Pat. No. 4,003,614 granted to Geer et al on Jan. 18, 1977 shows a door mounted hook operated by a handle 16 to engage a transversely extending keeper 26. The hook extends through an opening in the cabinet wall, rendering the structure unuseable in the present context.
U.S. Pat. No. 2,789,851 granted to Lickteig on Apr. 23, 1957 is another high friction hook and latch arrangement for clamping a swinging window tightly against a window sill. As suggested above, this structure will not be useful for sealing cabinets like those described herein.
U.S. Pat. No. 3,262,726 granted to Phelps on July 26, 1966 and U.S. Pat. No. 3,490,804 granted to Little on Jan. 20, 1970 both show latch mechanisms to hold casket covers down hard against a gasket or other sealing device. These are ineffective because they are just a hook and latch arrangement where brute force is used to overcome excessive friction. Since they relate to caskets, these structures, after all, only have to be sealed one time and then must hold "forever." They will not be useful to provide the over-and-over, repeated operation which the latch apparatus of the present invention must provide.
U.S. Pat. No. 2,901,277 granted to Anderson on Aug. 25, 1959 is another simple hook shape latch and keeper arrangement but one that is spring loaded. It is effective in all probability for use on the refrigerator door for which it is designed. However, it cannot be adapted to provide several latch points along the latch edge of a door and door frame. Also, the structure is not such as to provide the same force toward opening the door as is provided to pull the door closed to compress a soft rubber sealing gasket.
What was needed before the present invention was a positive door latch and release apparatus which would "take hold" at the time a door first came into contact with a solid strip of metal gasket on the hinge and latch edges of a door frame; would operate to pull the door powerfully, positively, and with little friction firmly down against the door frame while compressing the gasket along the latch edge and the hinge edge of the frame; and then, when the action of the handle is reversed, would positively push the door away from the frame until it was clear of the frame and the gaskets along the hinge and latch edges of the frame.
Neither the inventor nor those in privity with him are aware of any prior art which is closer than that discussed above, or of any prior art which anticipates the claims set out herein.